This invention relates to a two-cylinder pump for heavy flowable materials, such as concrete, the pump having a shutter mechanism which is pivotable across an apertured face plate, the shutter mechanism being sealed against the face plate by means of a cutting ring which is axially movable relatively to the shutter mechanism and is supported thereon with its rear side engaging a rectangular-section flexible rubber ring, whereby the cutting ring is urged resiliently aginst the face plate.
Such pumps must handle material which to a relatively large extent usually consists of hard particles of varying sizes, which in concrete comprise grains of sand and grit. In operation the shutter mechanism carries out periodic movements in rhythm with the piston strokes in the cylinders, so as to connect the output cylinder with a delivery conduit and the input cylinder with a storage container. The cutting ring provides a seal against the face plate, and also breaks up solid particles which are present in the material and which get in the way of parts moving in relation to each other when the shutter mechanism moves. Therefore the cutting ring must be urged against the face plate with considerable pressure. On the other hand, it must be able to move relatively to the face plate and the shutter mechanism to compensate for wear of itself and the face plate.
It is known that the cutting ring can be prestressed mechanically by the shutter mechanism (German Offenlegungsschrift No. 23 62 670). For this purpose the shutter mechanism, in the form of a swinging pipe, is resiliently connected by means of a swivel arm to a control shaft which is axially movable for prestressing the swivel arm. However, this has the disadvantage that flexible distortion of the mechanical parts produces a gap adjacent the face plate, and compensation for large amounts of wear of the face plate and the cutting ring is not possible.
It is further known that this mechanical prestressing can be replaced by hydraulic prestressing (German Offenlegungsschrift No. 28 35 590), which is variable in such a way that a greater contact pressure is produced when the shutter mechanism, in the form of a swinging pipe, is aligned with one of the cylinder openings. From beginning to end of the swinging motion, on the other hand, there is little contact pressure. This results in the formation of a gap, which is dangerous due to the hard particles in the material being transported. Moreover, prestressing by oil pressure is questionable on account of possible contamination of the concrete by the hydraulic liquid.
In a further improved solution (German Offenlegungsschrift No. 26 32 816), the cutting ring is prestressed without stressing the shutter mechanism, which is in the form of a swing pipe connected to the above-mentioned swivel arm, in that the cutting ring is connected to a joint on the swivel arm. However, by this means large amounts of wear on the cutting ring and on the face plate cannot be compensated for in all directions, so that sooner or later it will no longer be possible to prevent the formation of a gap.
It is known from German Offenlegungsschrift No. 29 03 749 that, by means of the hydrostatic force of the material being transported, the shutter mechanism, which is in the form of an S-shaped swing pipe, can be pressed resiliently against the face plate hydrostatically and by the axial compression of a rectangular section sealing ring clamped on the delivery conduit. However, the mechanical compression of the flexible rubber ring only produces low axial forces, since the seatings allow the flexible rubber ring to deflect inwardly along the whole axial length of its inner surface. In this device the cutting ring is supported on a bearing in which spherical surface interact with each other in order to give the cutting ring freedom of movement, which allows compensation for wear on the face plate and cutting ring.
The arrangement of the sealing ring, the swing pipe and its S-shape all lead to difficulties in carrying out the desired operations.
The viscosity of the material being transported in this type of swing pipe causes a drop in pressure to a specific degree. Also, in operating the pump the pressure drop can suddenly increase considerably, for example if the shutter mechanism becomes clogged up. In this case, the cutting ring is only prestressed resiliently and therefore with much too low a force. The gimbal bearings of the cutting ring for their part present considerable difficulties.
This invention therefore proceeds from a previously known solution (German Offenlegungsschrift No. 26 14 895). This is based on the concept of, on the one hand, achieving the hydrostatic differential pressure, which presses the cutting ring with increased force on to the face plate, by means of a lesser stressing of the sealing surface of the cutting ring by the hydrostatic pressure of the flowable material in favour of a greater stressing of the rear side of the cutting ring with this pressure and, on the other hand, of prestressing the sealing ring necessary for sealing the cutting ring radially, which sealing ring can also be rectangular in cross-section, in such a way that the sealing ring can for its part easily resiliently prestress the cutting ring. However, when in operation, this radial prestressing is not convertable into any significant prestressing of the cutting ring on to the face plate. Since the pump must work not only in a compression operation but also in a suction operation, however, the sealing ring is often lifted from its seating during the suction operation of the pump and gets lost in the flowable material.
Moreover, there is also the disadvantage that the flexible rubber sealing ring and the cutting ring are only prestressed by the hydraulic pressure, since during the swinging movement of the shutter mechanism insufficient pressure of the cutting ring on to the face plate is achieved. Compensation for wear is only possible by retightening the swing pipe bearing by means of several tie rods. However, this can incur considerable risks to the pump, since even a slight deviation of the swivel axis from its predetermined position can lead to significant damage and destruction of the shutter mechanism. Large amounts of wear cannot be compensated for on the cutting ring, so that the formation of a gap is automatically caused by wear. Moreover, with metallic expanding devices which are used with a sealing ring consisting of an elastomer, it is not possible in practice to prevent this ring being lifted from its seating.
The object of the present invention is, with a pump of the latter-mentioned type, to achieve a reliable compression of the cutting ring on the face plate even during operation of the shutter mechanism, and automatic compensation for wear of the face plate and cutting ring, without any fear of losing the flexible rubber ring.